In recent years the close circuit television (CCTV) industry has grown tremendously, with the likelihood of continued growth in future years. Future growth could enable the CCTV industry to provide hundreds, possibly thousands of intelligent transportation systems (ITS) and security systems to be installed. As the CCTV and security industry base grows, it has become increasingly important to minimize breakdowns in security systems in order to avoid loss of protection to customers. One way to accomplish this is to simplify circuits and to minimize the number of circuit components required to achieve a given function.
In the art of video switching technology, it is typical to switch from a wide array of signal sources to a single output bus or buses in series, such as a bus structure coupled to a single video monitor or to a broadcast channel. Various routing switchers are available in the marketplace, and these switchers often include complicated switching circuitry or dedicated control logic circuits for switching from a large number of input sources to a series of output buses. More particularly, the problem faced was one of designing complex logic control of multiple matrix buffer amplifiers sharing the same bus structure.
Such applications require the ability of the bus drivers to apply video signals from intermediate buses to the output bus with a relatively low source or sink impedance and to isolate video signals from the bus with a relatively high “off state” impedance. Such a characteristic is called a “tri-state” operation because three drive conditions are possible comprising: (1) supplying or “sourcing” current to the bus with a low impedance, (2) removing or “sinking” current from the bus with a low impedance or (3) isolating or de-coupling the video signal from the bus with a very high impedance, essentially an open circuit.
Hence, it is desirable to provide a simpler and more reliable circuit that is capable of switching from numerous inputs on an intermediate bus to a common output bus handling the signals from a number of intermediate buses without the need for dedicated control logic. One such example is the System6E Matrix Routing Switcher, manufactured by Cybermation Systems, Inc. of British Columbia, Canada, the assignee hereof. The System6E Video Routing Switcher is capable of full matrix switching 1280 inputs by 256 outputs in one single device. In order to accomplish this, a new self-directing bus buffering circuit is needed.